I would take both and connect to a short piece of track to troubleshoot this. Eliminate the layout and the wiring. Zero in on what's working and where the problem is.
Maybe you could swap the TIU #4 with TIU #3 for example and see what works. Do you get voltage right now to the track where TIU #4 is? Was this TIU used? Did you reset it? (or make sure the DCS signal is turned on)